The advent of uniform nanoparticles has made a significant impact on many different technological areas such as high density magnetic data storage elements, high density single-electron transistor devices and highly efficient laser beam sources. These nanometer-sized particles possess new and interesting electrical, magnetic and optical properties compared to the existing and widely known particles in the sizes larger than micrometer range.
The surface property of nanoparticle materials is very critical, because nanoparticles have high surface to volume ratio and high surface defect ratio in comparison with bulk materials. In addition, quantum confinement effect of nanoparticles, which have intermediate sizes between molecules and macroscopic bulk materials, has increased the scientific and technological interests. These nanoparticles find applications in nanodevices, nonlinear optical materials, catalysts, and data storage devices. In particular, in the era of information and multimedia, there are increasing demands for the development of magnetic data storage devices with high density, high speed, low electrical power consumption, and ultra-low weight. Recently intensive research has been conducted for the development of magnetic storage devices using magnetic nanoparticles. As a result, the synthesis of monodisperse nanoparticles with controllable sizes has been intensively pursued. However the synthesis of monodisperse magnetic nanoparticles turned out to be very difficult because of strong electromagnetic interaction between nanoparticles. [Science, 267 (1995) 1338, Journal of Applied Physics, 61 (1987) 3323, IEEE Transactions on Magnetism, 27 (1991) 5184]
Maghemite(γ-Fe2O3), a ferrimagnetic iron oxide material, has been commonly used as magnetic storage media for commercial magnetic tape and hard disk device applications since 1937, and even today it is being used widely as an important magnetic material essentially for storage media. However, due to the fact that the size of the existing maghemite particles are in the range of micrometers and the minimum area required for a magnetic storage element is determined by the size of the magnetic particles, the density of the magnetic media is limited by the size of the magnetic particles.
Recently, intensive research has been conducted for synthesizing uniform nanometer-sized magnetic nanoparticles for their applications to high density magnetic data storage media. In the conventional magnetic data storage media, the minimum magnetic storage element, which is called a magnetic domain, is the minimum magnetic unit oriented along the applied magnetic field, and the conventional magnetic storage element is an aggregate of many small crystals of magnetic materials. However, unlike the conventional magnetic data storage media, the nanoparticles with uniform size and shape, if used as magnetic storage media, increases the storage area density significantly, whereby a magnetic storage density of so-called multi-terabits/in2 based on the prospect of one particle-on-one bit system can be achieved. There exist already various synthetic methods for producing uniform spherical magnetic nanoparticles. Some of the examples are “Thermal decomposition of organometallic precursors”, [Journal of Physical Chemistry, 84 (1980) 1621], “Sonochemical decomposition of organometallic precursors”, [Journal of American Chemical Society, 118 (1996) 11960], “High temperature reduction of metal salts”, [Journal of Applied Physics, 85 (1999) 4325, also Korean Patent KR2000-0011546], and “Reduction of metal salts in reverse micelles”, [Journal of Physical Chemistry B, 103 (1999) 1805].
In particular, “Method of short-burst of nucleation induced by rapid injection of precursors into a hot surfactant solution followed by aging”, [Journal of American Chemical Society, 115 (1993) 8706], has been most widely used for synthesizing monodisperse nanoparticles. In other methods, rod-shaped magnetic nanoparticles were synthesized through the use of oriented growth of spherical nanoparticles [Journal of American Chemical Society, 122 (2000) 8581] and [Science 291 (2001) 2115].
However, the size of the nanoparticles produced using these synthetic methods is not uniform. In addition, compared to the nanoparticles of II-VI semiconductors and noble metals such as gold, silver, and platinum, relatively very little research has been conducted for the synthesis of monodisperse nanoparticles of transition metals and oxides. Also, it is a well-known fact that synthesizing uniform nanoparticles in their size and shape is not an easy task.
Meanwhile, Alivisatos, et al. disclosed the synthesis of nanoparticles of transition metal oxides such as iron oxide[gamma-Fe2O3, maghemite], manganese oxide[Mn3O4] and copper oxide[Cu2O] by thermally decomposing metal Cupferron[N-nitrosophenylhydroxylamine[C6H5N(NO)O−] precursors at high temperature in the presence of surfactant. However, the resultant nanoparticles are irregular in size and their crystallinity is very poor, and therefore, it is very difficult to form superlattices for the applications to magnetic data storage media. In addition, very expensive metal Cupferron complex precursor is used [Journal of American Chemical Society, 121 (1999) 11595].
Therefore, the main objective of the present invention is to disclose a method of synthesizing nanoparticles that overcome the deficiencies aforementioned.